The use of containers for packaging various beverages and other products has been common practice for many years. In recent years a new type of container has been developed which is commonly referred to as a "two-piece" container. In the formation of this type of container, a disc is drawn and ironed or extruded to form a cup which defines the bottom and side walls of a container. The free edge portion of the container body usually has a flange formed thereon which is utilized to attach an end panel to produce the finished product.
In the formation of this type of container, it is extremely important that the flange be devoid of any imperfections which may result in leakage after the container body and end panel have been seamed to each other.
Various types of proposals have been suggested for testing different portions of containers for flaws or imperfections. However, because of the speed at which the present day machinery is being operated, many of these devices are impractical for use on a production line.
While various methods of detection have been proposed, the speed and repetition rate in the formation of containers dictates that only non-contact test methods be used for detecting any flaws or imperfections.
One type of non-contact test that has been developed is known as the optical system wherein a light source is utilized as a portion of the test equipment. It has been found that such optical sytems must be quite sophisticated in order to produce an acceptable system which is not affected by ambient light, dirt or other variations.
Another type of test apparatus utilizes ultrasonics for detecting imperfections. However, this approach seems to be impractical due to the small dimensions of the cracks and the proximity of the cracks or imperfections to the edge of a flange.
The third type of non-contact system utilizes eddy currents as a sensing means. Various types of inspection apparatus have been proposed for inspecting various aspects of containers, and examples of such devices are shown in U.S. Pat. Nos. 3,700,101; 3,831,084; 3,609,527; and 3,495,166. While all of the above patents utilize the basic concept of eddy current detection of various types of flaws, none of these systems to date are capable of being utilized directly with a production line wherein containers must be checked in a short span of time.
Thus, there remains a need for a simple and inexpensive mechanism for detecting imperfections in containers and one which can be utilized as part of the production line in container manufacturing plants.